1. Technical Field
The present invention relates generally to mechanisms for electrolytic plating and, more particularly, to an anode container, electroplating system, method and object so plated.
2. Related Art
Electrolytic plating system anode containers often consist of an open mesh type structure or basket that contains anode material, sometimes in the form of spheres, that provide electrical contact between anode material and flow of plating solution through the array of anode material. See, for example, U.S. Pat. Nos. 4,059,493 and 4,569,744 to Rice and Walker, respectively. During the electroplating process, anode materials are consumed over time. These baskets commonly have a limitation, that as the anode material dissolvesand the remaining anode material descends toward the bottom of the basket, a bridge or arch will form, preventing the material from descending further in the basket. When a basket having parallel faces is loaded with a particulate medium, such as spheres, an outward pressure is applied to the faces of the anode container and the container faces deform outwardly. Unfortunately, the anode material does not pass the point of maximum deformation, hence, creating a self-supporting bridge or arch area. If there are holes, braces, or supports in the basket, the chance of a bridge or arch is increased. When a bridge or arch is created, the anode material must be removed or repositioned to disassemble the bridge, hence, slowing the overall processes.
If the bridge or arch is not removed, variations in plating thickness can occur. Since the plating ions take the path of least resistance, i.e., the shortest distance, two mechanisms occur to alter the plating deposit. First, the anode material at or below the bridge or arch in the anode container can be depleted reducing available ions with no replacement material passing the bridge or arch. Secondly, the electrical circuit can be disturbed to the lower portion of the anode container, reducing current flow through the anode material below the bridge or arch. Both of these situations reduce the plating in the same region of the plating cell or object(s) being plated. Since most plating systems are time and current controlled, the plating above the bridge or arch in the anode container is increased to compensate for the reduced plating below the bridge or arch, increasing the overall variability of the plating deposited on the object(s).
Previous anode baskets have used expanded mesh members to provide plating solution flow and ion transport. Sometimes, a sheet of metal, such as titanium, is slit and expanded to create the basket by plastic deformation. Unfortunately, the deformation of the slit sheet of metal creates out-of-plane areas in the side of the basket which catch on the anode material. Where the baskets are created by slitting plastic sheets, the baskets are not as strong. See, for example, U.S. Pat. No. 5,340,456 to Mehler.
One way of promoting anode material motion has been to apply a shock or vibration to the anode basket. See, for example, U.S. Pat. No. 3,862,745 to Chiz and U.K. Patent No. 315,481 to Collingridge. Where the baskets are mesh or contain welded joints, the vibration mechanisms can deform the basket and/or break welded joints within the basket. In the case where vibration is applied to the anode material above a bridge or arch, these additional loads are transmitted by the bridge or arch to the face of the anode container, further deforming the container and breaking weld joints.
In view of the foregoing, there is a need in the art for an electroplating system having a strong anode-receiving container that prevents anode bridging and arching.